The present invention relates to a flame-retardant polyester resin composition, molded products thereof and a molding method therefor and, more specifically, to a flame-retardant polyester resin composition which has excellent heat resistance, flame retardancy and moldability, molded products thereof and a molding method therefor.
Polyester resins have been increasingly used in electric and electronic parts, auto parts and mechanical parts thanks to their excellent heat resistance, mechanical properties and chemical resistance. In the field of electric and electronic parts, flame retardancy is also strongly sought for from the viewpoint of safety against fires and a composition comprising a flame retardant is used.
Although brominated polycarbonate oligomers and brominated epoxy oligomers have been studied as flame retardants for polyester resins, excellent moldability such as high fluidity and residence stability have been required of polyester resin compositions to meet demand for lightweight and small-sized electric and electronic parts as well as demand for improved productivity.
The brominated polycarbonate oligomers which have been widely used as a flame retardant for polyester resins have such problems as poor fluidity and low residence stability because it causes an ester exchange reaction with a polyester. The brominated epoxy oligomers have such a defect that their viscosity is considerably increased by residence due to a reaction between the terminal epoxy group thereof and the terminal carboxyl group of a polyester particularly when they contain antimony trioxide as a flame retarding aid though they have high fluidity.
To solve the above problems of the brominated epoxy oligomers, JP-A 58-118849 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses use of a brominated epoxy compound having an average polymerization degree of 11 or more and JP-A 62-169847 discloses use of two different brominated epoxy compounds having polymerization degrees of 20 or more and 0 to 10.
Although various attempts have been made to reduce reactivity by capping the terminal epoxy group of the brominated epoxy compound with another compound, a new step for capping the terminal is necessary, thereby losing economical efficiency.
Meanwhile, brominated polyacrylates are used as a flame retardant for polyester resins and have excellent fluidity. However, brominated polyacrylates do not show sufficient residence stability due to an ester exchange reaction with a polyester resin.
In recent years, importance has been attached to use of regenerated materials and recovered materials as part of efforts to improve productivity. JP-A 10-130481 discloses that even when a polyester resin composition which is flame retarded with a brominated polyacrylate is molded using a large amount of its regenerated material, the obtained molded product has excellent characteristic properties. However, both brominated epoxy compound-containing polyester resins and brominated acrylate-containing polyester resins have such a problem that changes in viscosity caused by the residence lead to fluctuations in molding conditions when a regenerated material is used, thereby reducing productivity.
With the technology of the prior art, use of a high molecular weight brominated epoxy compound reduces the fluidity of a resin and use of a low molecular weight brominated epoxy oligomer in combination with the above brominated epoxy compound does not improve the residence stability of a composition completely. Thus, it is difficult to achieve both fluidity and residence stability at the same time.
When a brominated epoxy compound is used to flame retard a resin, use of a polymer having a small amount of a terminal carboxyl group as a polyester resin which reacts with the epoxy group is effective to some extent but still unsatisfactory to adopt broader molding conditions.
The present invention has been made in view of the above circumstances.
That is, it is an object of the present invention to provide a flame-retardant polyester composition having excellent moldability such as fluidity and residence stability.
It is another object of the present invention to provide a method of molding the above flame-retardant polyester composition of the present invention.
It is still another object of the present invention to provide a molded product of the above flame-retardant polyester composition of the present invention.
The further objects and advantages of the present invention will become apparent from the following description.
Firstly, according to the present invention, the above objects and advantages of the present invention are attained by a flame-retardant polyester composition (may be referred to as xe2x80x9cfirst composition of the present inventionxe2x80x9d hereinafter) comprising;
(A) 100 parts by weight of an aromatic polyester having a terminal carboxyl group concentration of 60 equivalents/ton or less;
(B) 5 to 50 parts by weight of flame retardants consisting of (B1) a brominated epoxy compound represented by the following formula (1): 
xe2x80x83wherein n is a number of 11 to 50,
and (B2) a brominated polyacrylate represented by the following formula (2): 
xe2x80x83wherein R is a hydrogen atom or methyl group, p is a number of 1 to 5, and m is a number of 20 to 160,
the (B1)/(B2) weight ratio being 5/95 to 95/5; and
(C) 2 to 20 parts by weight of antimony trioxide.
Secondly, according to the present invention, the above objects and advantages of the present invention are attained by a flame-retardant polyester composition (may be referred to as xe2x80x9csecond composition of the present inventionxe2x80x9d hereinafter) comprising the above components (A), (B) and (C), and
(D) 5 to 100 parts by weight of a fibrous inorganic filler.
Thirdly, according to the present invention, the above objects and advantages of the present invention are attained by a method of producing a molded product of a flame-retardant polyester composition, characterized in that the flame-retardant polyester composition is a mixture of 50 to 75 wt % of the first composition or the second composition of the present invention which is not used for molding yet and 50 to 25 wt % of the first composition or the second composition of the present invention which contains the same type of a flame retardant in the same amount as the above composition and which has already been used for molding and recovered.
In the fourth place, according to the present invention, the above objects and advantages of the present invention are attained by use of the first composition or the second composition of the present invention which has already been used for molding and recovered as a raw material to be mixed with the first composition or the second composition of the present invention which is not used for molding yet to produce a molded product.
Finally, according to the present invention, the above objects and advantages of the present invention are attained by a molded product of the first composition or the second composition of the present invention.
The present invention will be described in detail hereinafter.
(A) Aromatic Polyester
The aromatic polyester as the component (A) used in the present invention comprises dicarboxylic acid components and diol components. The dicarboxylic acid components include terephthalic acid, isophthalic acid and phthalic acid; phthalic acid derivatives such as methyl terephthalate and methyl isophthalate; and naphthalenedicarboxylic acid and derivatives thereof such as 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and 1,5-naphthalenedicarboxylic acid. The diol components include aliphatic diols such as ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol and neopentyl glycol.
Preferred examples of the aromatic polyester (A) include polytetramethylene terephthalate, polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate and polytetramethylene-2,6-naphthalene dicarboxylate. Out of these, polytetramethylene terephthalate is particularly preferred because it is excellent in the balance between characteristic properties and moldability.
An aromatic polyester prepared by substituting part of the above polyester with a copolymerizable component may be used as the aromatic polyester. The amount of the copolymerizable component is preferably 10 mol % or less based on the total of all the dicarboxylic acid components.
Further, the above aromatic polyesters may be used in combination of two or more.
The aromatic polyester used in the present invention has a terminal carboxyl group concentration [COOH] of 60 equivalents/ton or less, preferably less than 30 equivalents/ton. The terminal carboxyl group concentration [COOH] is measured by an A. Conix method (Makromol. Chem., vol. 26, pp. 226, 1958). When the terminal carboxyl group concentration is higher than 60 equivalents/ton, a reaction between the aromatic polyester and the brominated epoxy compound as the component (B) becomes marked, thereby making it difficult to obtain the effect of the present invention. When an aromatic polyester having a terminal carboxyl group concentration of less than 30 equivalents/ton is used, moldability further improves advantageously.
The intrinsic viscosity of the aromatic polyester used in the present invention is 0.5 or more, preferably 0.6 to 1.2, particularly preferably 0.7 to 1.0 when it is measured in o-chlorophenol at 35xc2x0 C.
The aromatic polyester having a terminal carboxyl group concentration of 60 equivalents/ton or less, preferably less than 30 equivalents/ton used in the present invention can be produced by a known method per se, such as one in which appropriate reaction conditions are selected in a melt polycondensation reaction or one in which a melt polycondensation reaction and a solid-phase polycondensation reaction are combined.
(B1) Brominated Epoxy Compound
The brominated epoxy compound as the component (B) used in the present invention is a poly(tetrabromo)bisphenol A epoxy compound represented by the following formula (1): 
wherein n is a number of 11 to 50.
This compound can be obtained by mixing tetrabromobisphenol A with tetrabromobisphenol A diglycidyl ether obtained by reacting tetrabromobisphenol A with epichlorohydrin in an amount of 0 to 0.96 equivalent in terms of the hydroxyl group based on 1 equivalent of the epoxy group and reacting them with each other by heating at 100 to 250xc2x0 C. in the presence of a basic catalyst such as sodium hydroxide, lithium hydroxide or tributylamine.
The average polymerization degree xe2x80x9cnxe2x80x9d of the brominated epoxy compound is 11 to 50, preferably 11 to 20. When the average polymerization degree is lower than 11, the epoxy equivalent of the brominated epoxy compound becomes large, thereby making it difficult to suppress a reduction in moldability caused by a reaction between the aromatic polyester and the brominated epoxy compound. When the average polymerization degree is higher than 50, the fluidity of the aromatic polyester lowers.
(B2) Brominated Polyacrylate
The brominated polyacrylate as the component (B2) used in the present invention is a polymer represented by the following formula (2), namely, a brominated benzyl acrylate or brominated benzyl methacrylate polymer: 
wherein R is a hydrogen atom or methyl group, p is a number of 1 to 5, and m is a number of 20 to 160.
Illustrative examples of the brominated polyacrylate include polypentabromobenzyl acrylate, polytetrabromobenzyl acrylate, polytribromobenzyl acrylate, polypentabromobenzyl methacrylate and the like. Out of these, polypentabromobenzyl acrylate is particularly preferred.
This brominated polyacrylate may be copolymerized with a small amount of another vinyl-based monomer. The amount of the vinyl-based monomer is preferably 10 mol % or less.
The average polymerization degree xe2x80x9cmxe2x80x9d of the brominated polyacrylate is 20 to 160, preferably 50 to 120. When the average polymerization degree is lower than 20, the heat resistance of the aromatic polyester lowers and when the average polymerization degree is higher than 160, the fluidity of the aromatic polyester lowers.
The total amount of the brominated epoxy compound (B1) and the brominated polyacrylate (B2) as flame retardants is 5 to 50 parts by weight based on 100 parts by weight of the aromatic polyester (A). When the total amount is smaller than 5 parts by weight, the effect of flame retarding the aromatic polyester becomes unsatisfactory and when the total amount is larger than 50 parts by weight, such a defect as deterioration in the mechanical properties of the composition appears. The blending ratio of the component (B1) to the component (B2) is 95/5 to 5/95, preferably 50/50 to 95/5. When the blending ratio is outside the above range, the moldability improving effect of the present invention is not fully exhibited.
(C) Antimony Trioxide
The amount of the antimony trioxide (C) is 2 to 20 parts by weight based on 100 parts by weight of the aromatic polyester (A). When the amount is smaller than 2 parts by weight, the effect of the flame retarding aid is not fully exhibited and when the amount is larger than 20 parts by weight, such a defect as deterioration in the mechanical properties of the composition appears. Antimony trioxide having a purity of 98% or more and a particle diameter of 0.1 to 5 xcexcm is preferred as the component (C). Antimony trioxide having a purity of 99% or more and a particle diameter of 0.5 to 3 xcexcm is particularly preferred.
(D) Fibrous Inorganic Filler
In the second composition of the present invention, the fibrous inorganic filler (D) is blended in an amount of 5 to 100 parts by weight based on 100 parts by weight of the aromatic polyester (A). Thereby, a composition which is superior to the first composition in heat resistance and mechanical properties is obtained advantageously.
Illustrative examples of the fibrous inorganic filler include glass fiber, carbon fiber, steel fiber, asbestos, ceramic fiber, potassium titanate whisker, boron whisker, aluminum borate whisker, calcium carbonate whisker and the like. They may be used alone or in combination of two or more.
Out of the above fibrous reinforcements, glass fiber is preferred. Any glass fiber may be used if it is generally used to reinforce resins. It is selected from among long fiber type (glass roving), short-fiber chopped strand and milled fiber.
Fibrous reinforcements such as glass fiber may be treated with a binder (such as a polyvinyl acetate or polyester binder), coupling agent (such as a silane compound, Volan compound or titanium compound) or other surface treating agent.
Other Components
A pigment and other compounding agents may be added to the composition of the present invention as required in such amounts that they develop their effects. The compounding agents include a powdery, particular or lamellar inorganic filler such as kaolin, clay, wollastonite, talc, mica, calcium carbonate, barium sulfate, glass beads or glass flakes.
The filler is blended as a reinforcement, surface modifier or modifier for improving electric and thermal properties. It should be blended in a range from the minimum amount for developing its effect by blending to an amount that the excellent characteristic properties and molding advantages of the composition are not lost by blending excessively.
Other flame retardants such as polycarbonate oligomers produced from brominated polystyrene, brominated polyphenylene ether and brominated bisphenol-A; halogen-containing compounds such as dimers of brominated bisphenyl ether, brominated diphthalimide compound and chlorinated hexapentadiene; phosphorus compounds such as red phosphorus and triphenyl phosphate; phosphorus-nitrogen compounds such as phosphonic acid amide; triazine compounds such as melamine, melam, melam, mellon, cyanuric acid and melamine cyanurate; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, dawsonite and gypsum dihydrate, and flame retarding aids other than antimony trioxide, such as metal oxides including antimony tetraoxide, antimony pentoxide, sodium antimonate, boron oxide and iron oxide may be blended in limits that do not impair moldability and the like. To further improve the effect of the flame retardant, a compound which suppresses dripping of molten particles at the time of burning may be blended. Examples of the compound which exhibits this effect include known polytetrafluoroethylene and fumed colloidal silica which are produced by emulsion polymerization.
To improve heat resistance, an antioxidant or thermal stabilizer such as a hindered phenol compound, aromatic amine compound, organic phosphorus compound or sulfur compound may further be added. To improve melt viscosity stability and hydrolysis resistance, an epoxy compound or oxazoline compound may be added. Preferred example of the epoxy compound include a bisphenol A type epoxy compound obtained from a reaction between bisphenol A and epichlorohydrin, aliphatic glycidyl ethers obtained from a reaction between glycols and glycerol epichlorohydrin, novolak type epoxy compounds, aromatic and aliphatic carboxylic acid type epoxy compounds, alicyclic compound type epoxy compounds and the like. The oxazoline compound is preferably an aromatic or aliphatic bisoxazoline, particularly preferably 2,2xe2x80x2- bis(2-oxazoline) or 2,2xe2x80x2-m-phenylenebis(2-oxazoline).
Other stabilizer, colorant, lubricant, ultraviolet light absorber and antistatic agent may also be added.
Further, a small amount of another thermoplastic resin, for example, another polyester resin, polyamide resin, polyphenylene sulfide resin, polyphenylene ether resin, polycarbonate resin, phenoxy resin, polyethylene or copolymer thereof, polypropylene or copolymer thereof, polystyrene or copolymer thereof, acrylic resin or acrylic copolymer, polyamide elastomer, polyester elastomer; or thermosetting resin such as phenolic resin, melamine resin, unsaturated polyester resin or silicon resin may be added.
Preferably, these compounding ingredients are uniformly dispersed in the resin composition of the present invention. Any compounding method may be used. For example, all or part of the compounding ingredients are supplied to a heated single or double-screw extruder en bloc or separately and homogenized by melt kneading and the obtained molten resin extruded into a wire form is solidified by cooling, cut to a desired length and granulated. A mixer such as a blender, kneader or roll may be used. These methods may be used in combination or repeated a plurality of times to add the compounding ingredients sequentially.
To obtain a resin molded product from the thus produced resin composition for molding, the resin composition is supplied to a molding machine such as an injection molding machine while it is fully kept dry. Further, the constituent raw materials of the composition may be dry blended and directly injected into the hopper of a molding machine to be melt kneaded together in the molding machine.
The resin composition of the present invention preferably exhibit its characteristic features in the molding method using a regenerated material or recovered material. The regenerated material is a ground product of a non-product part such as a sprue or runner generated at the time of molding or pelletized product obtained by re-extruding it.
Although use of the regenerated material is effective in making use of resin composition raw materials and reducing the amount of waste, the resin composition is molten repeatedly, whereby the characteristic properties of the resin tend to deteriorate.
Underwriter Laboratories (UL) of the US which authorizes the characteristic properties of plastic materials permits use of 25 wt % or less of a regenerated material as a raw material for a molded product. When a regenerated material is used in an amount of more than 25 wt % as a raw material for a molded product, confirmation is required separately.
When a composition obtained by flame retarding the aromatic polyester (A) with the brominated epoxy compound (B1) is molten repeatedly, a phenomenon that its melt viscosity increases appears markedly. Since use of a regenerated material inevitably involves re-melting of the regenerated material, it has been difficult to use a material regenerated from the composition. A composition obtained by flame retarding the aromatic polyester (A) with the brominated polyacrylate (B2) has poor residence stability and experiences a great reduction in melt viscosity. Therefore, it has been difficult to use a material regenerated from this composition as well.
However, the resin composition of the present invention has high residence stability while retaining high fluidity. Even when a regenerated material is used for molding in an amount of more than 25 wt %, the advantage of high residence stability can be obtained. The amount of a regenerated material used is preferably 50 wt % or less. When the amount of a regenerated material is more than 50 wt %, the characteristic properties of the resin composition of the present invention greatly lower disadvantageously.
The present invention further provides a molding method using a regenerated material in an amount of more than 25 wt % and 50 wt % or less as a raw material for molding when a flame-retardant polyester resin composition is to be molded. It is a fundamental rule to use a resin composition containing the same type of flame retardant in the same amount as a regenerated material. Additives may be added in small amounts that do not impair the characteristic properties of the resin composition of the present invention.
In other words, the molding method of the present invention is a method of producing a molded product from the flame-retardant polyester resin composition of the present invention in an amount of 50 wt % or more and less than 75 wt % based on the total weight of all the raw materials as a raw material for molding and a material regenerated from the flame-retardant polyester resin composition in an amount of more than 25 wt % and 50 wt % or less based on the total weight of all the raw materials as a raw material for molding.